1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a direct type backlight unit and an LCD device having the same that have a reduced number of lamps and an external electrode having an extended longitudinal length.
2. Discussion of the Related Art
A cathode ray tube (CRT) device, one of the most widely used display devices, has been used in televisions, measurement instruments, and information terminals, but a CRT device has a relatively heavy weight and a large size. Thus, a CRT device cannot actively meet the current small-sizing and lightweight product requirements.
To replace such a CRT device, an LCD device having the advantages of small size, light-weight, and low power consumption has actively developed. In addition, an LCD device can provide a high contrast ratio for displaying a gray scale or a moving image. Thus, an LCD device has expanded applications as a display device.
However, since an LCD device does not generate light by itself, it requires a separate external light source for generating light. Thus, an LCD device displays an image by controlling light generated by the external light source, e.g., a backlight unit, that is illuminated on an LCD panel.
In general, the backlight units are classified into an edge type and a direct type according to the position of a light source relative to a display plane. In particular, the direct type backlight unit has a high light use rate, imposes no limitation in the size of the display plane and can be easily handled. Thus, the direct type backlight unit is widely used for a large-sized LCD device, e.g., an LCD device of more than 30 inches.
The direct type backlight unit does not require a light guide for converting linear light from a lamp into plane light and includes a plurality of lamps provided at a lower portion of the display plane, a reflection sheet for reflecting light from the lamp to the display plane to prevent light loss, and a diffuser plate for scattering the light to an upper side of the lamps to emit light uniformly. The lamps include one of a point light source, such as an incandescent lamp and a white halogen lamp, a linear light source, such as a hot cathode fluorescent lamp, a cold cathode fluorescent lamp, and an external electrode fluorescent lamp (EEFL), and a planar light source, such as an LED of a matrix shape.
Currently, the cold cathode fluorescent lamp (CCFL) is mainly used, but an external electrode florescent lamp (EEFL) is gradually replacing the CCFL. Since an EEFL has brightness of more than 400 nit, which is 60% greater than brightness of a CCFL, the EEFL can expand the TFT-LCD application field such as TV. In addition, unlike a CCFL having electrodes within lamps, an EEFL has external electrodes and thus is advantageous in operating in parallel, such that a uniform brightness can be realized by reducing a voltage deviation between the lamps. Further, inverters that are required for driving a plurality of EEFLs can be reduced because EEFLs have external electrodes. As a result, the number of parts of the backlight unit is reduced, and the manufacturing cost and the weight of the LCD module can be remarkably reduced.
FIG. 1 is an exploded perspective view illustrating a direct type backlight unit of an LCD device according to the related art. In FIG. 1, a direct type backlight unit 100 includes a plurality of lamps 101, a bottom cover 102 for seating the plurality of lamps 101 at an interval, a reflection sheet 103 disposed under the lamps 101 for reflecting light generated from the lamps 101 to a front side of the backlight unit 100, a diffuser plate 105 disposed on the lamps 101 for diffusing light, and a diffuser sheet 106 disposed on the diffuser plate 105 for enhancing the diffusion of light. The lamps 101 are linear lamps, and the direct type backlight assembly 100 does not separately require a light guide.
FIG. 2 is an exploded perspective view illustrating a linear type lamp unit of the direct type backlight unit shown in FIG. 1, and FIG. 3 is a plan view illustrating the lamp unit shown in FIG. 2. As shown in FIGS. 2 and 3, external electrodes 101a and 101b for applying a drive voltage are attached at both ends of the plurality of linear type EEFLs 101. The lamp unit also includes lamp support members 201, 202, 203, and 204 having holes 201a, 202a, 203a, and 204a for receiving the external electrodes 101a and 101b at both sides of the lamps 101. The lamp support members 201, 202, 203, and 204 have conductive layers 201b, 202b, 203b, and 204b for applying a voltage.
In addition, the external electrodes 101a and 101b form a bezel region, shown as shaded portions of the lamps 101, that blocks light. In particular, each of the external electrodes 101a and 101b has a length corresponds to a width of the holes 201a, 202a, 203a, and 204a, and has a width extending beyond the lamp support members 201, 202, 203, and 204 to supply a sufficient current to drive the lamp. However, when the width of each of the external electrodes 101a and 101b is extended in order to drive the EEFL, the bezel region also is widened. As a result, a non-light-emitting region also is widened, thereby reducing an effective light-emitting region of the backlight unit.